Fejér László - Lászlóffy Woldemár: A hidrometria magyarországi fejlődése (1700-1945) (Vízügyi Történeti Füzetek 13. Budapest, 1986)

Idegen nyelvű összefoglalók

Making use of data given by numerous measurements which were performed in the Budapest cross-section of the Danube during and after a flood, he tested the formulae of mean flow velocity and discharge used in international practice, expounding their practical value with respect to the Danube. Nearly a year after Ignác HORVÁTH's measurements a theoretical study written by young Jenő KVASSAY, later organizátor of the Hungarian civi.1 engineering service on the interrelation between the speed of revolution of a current meter and of flow velocity was published in the columns of the Annales des Ponts et Chaussées (1877). In fact, this was the first scientific discussion in respect of the shape of vanes of a current meter, * In the 70s and 80s of the last century regular hydrographie data provision was required increasingly by both the Hungarian practitioners in hydraulic construction and the river authorities responsible for flood control. A serious impetus was given to the matter of regular hydrographic observations by the devastating flood, too, that afflicted the city of Szeged in 1879. For the hydrographie service which was established in 1866, an important duty had been — beyond the regular provision of hydrographie data — the survey and permanent review of changes in the bed conditions of rivers, caused by regulation works. The execution of this task necessitated the performance of numerous flow velocity measurements. By 1898 the total number of discharge measurements executed on the Tisza river and in a smaller extent on the Danube and over 9 tributaries amounted to one thousand. In the course of this large-scale work Sámuel HAJÓS, later leader of the Hungarian hydrographie service, developed an instrumentation and measurement method of his own, considerably different from the one used generally abroad. The new construction of the HAJÓS-type current meter included, among others, two spiral vanes of different pitches, without spokes, and a device for rotation measurements. This instrument became well-known internationally and beside its domestic use it was in use also in the Russian hydrographie service for a long time. The elaboration of a so-called ,,detailed" measurement method is also connected to the name of HAJOS. This method was an improved version of the integrating measurement; here the signals of rotation during the uniform-rate lowering of the instrument, and of the time elapsed were written by a Morse device on a paper tape. The tape was sent on by a drum, which was connected to the lowering winch, proportionately to the distance negotiated by the instrument. After measurement, the flow velocity in the surroundings of optional points along a vertical could be determined in the knowledge of rotations and of the time signs on the tape and of the length of the unwound tape. The calibration of the current meters (the determination of coefficients of the rating equation) took place by a traction of the meter in still water, at a known velocity. Initiated by an attack against the results of its discharge measurements, the hydrographie service started a series of experiments aimed at clarifying the accuracy of discharge measurements (1891). Supported by the results of measurements, Sámuel HAJÓS, leader of the experiments, stated that the errors of measurements related to each other remained under 2 to 3%, while the results of measurements checked by the accurate volumetric method indicated the presence of errors between +1.5% and —3%.